Tar sand, also referred to as oil sand and bituminous sand, is a naturally occurring sedimentary rock which contains extractable amounts of bitumen or other very heavy oils in association with sand grains. The rock may be consolidated or unconsolidated. These terms refer to the presence or absence, respectively, of the structural integrity of the mineral component of the rock independent of the adhesive effect of the organic component. Some tar sand deposits, such as those found in Canada, are characterized by an envelope of water, sometimes called connate water, surrounding the sand particles. The water envelope in turn is surrounded by a film of bitumen. Other deposits, particularly those in the United States such as, for example, those from the Sunnyside deposit in Utah, lack the water envelope. The extraction process chosen to remove the bitumen will depend in part on whether the water envelope is present or absent. For example, a hot water separation process has been used extensively for the water-wet tar sands found in Canada. However, this approach is not effective for oil-wet tar sands.
In some processes for recovering the bitumen from the tar sand, the raw feed is ground to a particle size sufficient to allow separation of the bitumen from the sand grains. This approach requires grinding the feed to a relatively fine particle size distribution. The additional grinding necessary to liberate the sand grains translates into increased energy requirements. The ground material is passed through a froth flotation chamber to recover the bitumen. A collector such as kerosene is usually present to facilitate the separation. Such processes generally leave a significant part of the bitumen with the mineral residue. In addition, the kerogen fraction may form an emulsion with water which is not easily separated. Solid fines, especially clay particles if they are present in the feed, are usually carried along with the bitumen making further separation steps necessary.
In other processes an organic solvent is used to dissolve the bitumen. However, solvent loss is usually high in such processes making them economically unattractive.